September 01, 2010

Mesmerising Mars

Following up on bits and pieces of news, I periodically find myself on one of
the Mars imagery sites, lost in wonder; it’s a time-consuming process. So, I
thought, why not, again,
lure readers of this blog to accompany
me on these extraordinary journeys? Scientific Frontline, a
site that I just discovered, compiles a wide variety of images into all kinds of
galleries, not just of things extraterrestrial. It’s from there that the
stunning image above comes, originally, of course, from NASA/JPL/University of
Arizona and the Mars Reconnaissance Orbiter. The description is as follows:

Dunes within a crater on Mars are visible in this HiRISE image. This crater
is located in the southern hemisphere where it was winter at the time this image
was taken. This observation documents new seasonal processes occurring on
dunes at this latitude, as well as other interesting phenomena. The bright tones
are interpreted as carbon dioxide or water frost. This is generally concentrated
on the east-facing slopes of the dunes, which are in shadow and therefore
cooler. Some dark spots on the dunes may be areas that have defrosted more than
surrounding terrain. Landslides and dark-toned streaks are seen on many of
the west-facing dune slopes. The general dune morphology indicates formation by
westerly winds. However, zooming in on the image shows smaller scale ripples
that appear to have been formed by winds blowing from the south and north.
[Written by: Nathan Bridges & Kelly Kolb]

Mars has a vast sea of sand dunes in the high latitude region encircling its
North polar cap, known as the North polar erg. These dunes are made up of basalt
and gypsum sand grains. In some regions of the North polar erg where the sand
supply is limited they take on an elongated crescent shape. The icy ground that
the dunes are on top of has irregular polygonal patterns. In other areas with an
abundant supply of sand the dunes are continuous (see also PSP_007494_2580).The
entire North polar erg is covered in the winter with a seasonal polar cap
composed of carbon dioxide (dry ice). In the spring time this seasonal polar cap
evaporates.[Written by: Candy Hansen]

And then, off we go into the stunning landscapes of the planet (it’s clearly
not geomorphology, but does anyone know the correct term?)

This observation shows a portion of the central sedimentary deposits in
Pasteur Crater. The deposits in this image now being eroded into knobs and
ridges. The erosion is probably dominated by wind, as most of the ridges are
parallel. This is common in wind-eroded features, with the ridges generally
aligned with the prevailing wind. At high resolution, layering is revealed
in many of the knobs and outcrops. The horizontal layers indicate that the
material was deposited uniformly over a broad area. Possible origins include
volcanic airfall or lacustrine (lake) deposits. After deposition, the rock in
this area has been fractured and faulted, forming a diverse array of cracks.
The mottled appearance of much of the image is caused by dark, featureless
patches which may be wind-blown dust. These have interacted with lighter-toned
ridges and ripples which are probably also formed by aeolian (wind) processes.
In places, the dark patches partially cover the ripples, indicating that they
have moved more recently, but they must be thin because the ripples frequently
stand above surrounding dark material. The ripples exhibit multiple
interacting orientations in some places, producing networks of small ridges
which reflect movement in winds from several directions. [Written by: Colin
Dundas]

We should not forget the European Space Agency project – the Mars Express high
resolution stereo-photography and mineral mapping mission (whose lander, the
Beagle 2, so ignominiously plummeted to the surface of Mars in 2003). The
imaging orbiter was originally expected to have a relatively short life, but its
operations have been extended several times and are continuing; its recent image
of Orcus Patera, a mysteriously elongated crater, has been in the news
last week ("scientists are baffled..."). I particularly like the image below (I have inserted a perspective detail)
from early on in the mission: a dune field in the crater Argyre Planitia. I
assume that the dark colour results from basaltic sands being constantly
reworked by the winds as opposed to being covered in dust, but why is the dune
field so compact and isolated? A reflection of the complex wind circulation
patterns? Note that 3D images are available from the website.

These images, taken by the High Resolution Stereo Camera (HRSC) on board
ESA's Mars Express spacecraft, show a Martian crater with a dune field on its
floor.The images were taken during orbit 427 in May 2004, and show the
crater with a dune field located in the north-western part of the Argyre
Planitia crater basin.

The images are centred at Mars longitude 303° East and latitude 43° South.
The image resolution is approximately 16.2 metres per pixel. The crater is
about 45 kilometres wide and 2 kilometres deep. In the north-eastern part of
this crater, the complex dune field is 7 kilometres wide by 12 kilometres long.
In arid zones on Earth, these features are called ‘barchanes’, [sic:
they mean, of course, “barchans”] which are dunes having an asymmetrical
profile, with a gentle slope on the wind-facing side and a steep slope on the
lee-side. The dune field shown here suggests an easterly wind direction with its
steeper western part. The composition of the dune material is not certain, but
the dark sands could be of basaltic origin.

I thought that you might share my enthusiasm - and yes, "geo-" is defined in the dictionary and normally used as denoting Earth, so we must find another term (although we do talk about "the geology of Mars etc., it's technically wrong).